Keep your Stihl FS 66 string trimmer running at its best with genuine OEM replacement parts from Repair Clinic. The Stihl FS 66 is a 27.2cc two-stroke gas string trimmer designed for light to medium brush cutting, using a Walbro carburetor and a straight shaft configuration that accepts a range of cutting attachments. As a two-stroke engine trimmer, the FS 66 relies on fuel-oil premix for lubrication, making it particularly vulnerable to carburetor varnish from fuel left in the system during storage. Repair Clinic stocks genuine Stihl OEM parts for the FS 66 including the Stihl trimmer carburetor parts, ignition coil, spark plug, and trimmer head. Browse the Stihl string trimmer parts catalog filtered by FS 66 for the complete parts inventory.
Stihl FS 66: Walbro Carburetor Variants and the 27.2cc Two-Stroke Service Universe
The Stihl FS 66 was produced across multiple years with three different Walbro carburetor part numbers: WT-45, WT-45A, and WT-112, making carburetor part number verification from the installed unit critical before ordering a replacement. The FS 66 shares the WT-45A carburetor with the FS 48, FS 52, FS 62, FS 81, FS 86, FS 88, and FS 106, making carburetor rebuild kits widely available for this family. As a two-stroke engine, the FS 66 requires a 50:1 fuel-oil premix in every tank. Ethanol content above 10% accelerates carburetor varnish formation and diaphragm degradation, which is why Stihl recommends using fresh fuel with fuel stabilizer or draining the carburetor before storage. The string trimmer repair help section covers FS 66 carburetor rebuild and trimmer head replacement.
Most Replaced Parts on the Stihl FS 66
Walbro Carburetor for the Stihl FS 66
Ethanol varnish deposits in the Walbro diaphragm carburetor are the most common cause of FS 66 performance problems after storage. The metering diaphragm and pump diaphragm harden with age and fuel exposure, reducing fuel delivery at both idle and full throttle. A carburetor rebuild kit replaces both diaphragms and needle valves for a fraction of the cost of a new carburetor and restores precise fuel metering.
Ignition Coil for the Stihl FS 66
The ignition coil on the FS 66 generates the high-voltage spark that ignites the fuel-air mixture in the 27.2cc cylinder. A coil that produces weak spark or no spark causes hard starting or complete failure to start even with a new spark plug. Testing for spark with a spark tester before replacing the coil confirms that the ignition system rather than the carburetor is responsible for starting failure.
Stihl FS 66 Trimmer Head
The trimmer head on the FS 66 uses bump-feed line advancement that extends trimmer line with each tap against the ground. A head that fails to advance line has a worn bump knob, worn spool, or line jammed inside the spool housing. Keeping the spool loaded with the correct 0.095-inch or smaller diameter line prevents the winding jams that cause most head failures on the FS 66.
Air Filter for the FS 66
The air filter on the Stihl FS 66 should be cleaned every 10 to 25 hours of operation and replaced annually. A clogged filter causes the FS 66 to run rich, producing black smoke from the exhaust and reducing full-throttle power during cutting. The FS 66 foam filter element can be washed with soap and water and dried before reinstallation.
Fuel Lines and Filter for the Stihl FS 66
The fuel lines and in-tank fuel filter on the FS 66 are direct contact with ethanol-blend fuel, which accelerates rubber degradation. Cracked fuel lines cause air leaks that prevent the carburetor from maintaining correct fuel pressure for the Walbro diaphragm system. Replacing all fuel lines and the fuel filter together when one shows visible cracking is the most cost-effective approach.
Why Choose Repair Clinic for Stihl FS 66 Parts
- Genuine Stihl OEM Components: WT-45, WT-45A, and WT-112 carburetor variants with clear production-run differentiation Stihl string trimmer parts.
- Carburetor Rebuild Kit Availability: Diaphragm and needle valve rebuild kits available as an alternative to complete carburetor replacement for cost-effective FS 66 servicing.
- Complete FS 66 Parts Inventory: Trimmer heads, ignition coils, and fuel system components for the full production run of the FS 66 Stihl string trimmer parts.
- 365-Day Returns: Return any uninstalled Stihl part within a full year of purchase with no restocking fees.
Stihl FS 66 String Trimmer Parts FAQ
What engine size does the Stihl FS 66 use?
The Stihl FS 66 uses a 27.2cc two-stroke engine, making it a medium-duty trimmer suitable for light to medium brush cutting tasks. It uses a Walbro carburetor, designated WT-45, WT-45A, or WT-112 depending on the production run.
What carburetor fits the Stihl FS 66?
The FS 66 uses Walbro carburetors across its production runs. The carburetor part numbers used on the FS 66 include 4126 120 0600 (WT-45), 4132 120 0600 (WT-112), and 4126 120 0610 (WT-45A). Confirm the carburetor part number from the label on your installed carburetor before ordering a replacement.
How do I replace the trimmer head on the Stihl FS 66?
Secure the shaft to prevent rotation, then unscrew the old trimmer head counterclockwise from the drive shaft. Align the new head with the shaft threads and tighten clockwise until snug. Many FS 66 heads use left-hand threads on the arbor bolt, meaning they tighten counterclockwise rather than clockwise.
How do I adjust the carburetor on the Stihl FS 66?
The FS 66 carburetor has three adjustment screws: H (high speed), L (low speed), and S (idle). The baseline settings are H at two turns out from lightly seated and L at one-and-a-half turns out. Fine tune by running the engine at full throttle for H and at idle speed for L, adjusting until the engine runs cleanly in each range.
